Braided lines make a big difference on any car, taking a lot of the spongyness out of the brake pedal as the pipes don't expand like the std rubber ones.
FRS had 324mm discs and is a popular conversion on cossie with the calipers and brackets to suit, or you can get brackets to use the 2wd 4 pot std calipers with the frs discs.
Defo worth getting grooved discs, these will wear the pads ever so slightly quicker but well worth the improvement as they constantly de glaze the pads ensuring a perfect surface.
Pad wise a very personal thing I like EBC yellowstuff, perfect from old grannies to track cars, the same pads most of the police pursuit cars use btw, a very clean pad too with no noise don't take warming up either, and have ace feeling.
Disc size dependant mostly on wheel size, but even std 2wd 4 pots are a big improvement over the 4wd calipers.
tabetha